Semiconductor transistors, in particular field-effect controlled switching devices such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or an Insulated Gate Bipolar Transistor (IGBT), have been used for various applications including but not limited to use as switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. Particularly with regard to power devices capable of switching large currents and/or operating at higher voltages, low on-state resistance Ron, high breakdown voltages Ubd, high robustness and/or good softness are often desired.
To achieve low on-state resistance Ron and high breakdown voltages Ubd, compensation semiconductor devices were developed. The compensation principle is based on a mutual compensation of charges in n- and p-doped regions, which are often also referred to as n- and p-doped pillar regions, in the drift zone of a vertical MOSFET.
Typically, the charge compensation structure formed by p-type and n-type regions is arranged below the actual MOSFET-structure, with its source, body regions and gate regions, and also below the associated MOS-channels that are arranged next to one another in the semiconductor volume of the semiconductor device or interleaved with one another in such a way that, in the off-state, their charges can be mutually depleted and that, in the activated state or on-state, there results an uninterrupted, low-impedance conduction path from a source electrode near the surface to a drain electrode arranged on the back side.
By virtue of the compensation of the p-type and n-type dopings, the doping of the current-carrying region can be significantly increased in the case of compensation components, which results in a significant reduction of the on-state resistance Ron despite the loss of a current-carrying area. The reduction of the on-state resistance Ron of such semiconductor power devices is associated with a reduction of the heat generated by the current in the on-state, so that such semiconductor power devices with charge compensation structure remain “cool” compared with conventional semiconductor power devices.
Meanwhile, switching losses of power semiconductor devices have become more important. Depending on device operation, output charge QOSS (or output capacitance COSS) and switching losses EOSS, respectively, stored in the space charge region formed in the off-state and during reverse bias, respectively, mainly determine the switching losses. The stored charge QOSS of semiconductor devices with charge compensation structures may be comparatively high. This may result in significant switching losses EOSS when significant parts of the stored charge Qoss are removed at high voltages across load terminals of the power semiconductor device. In addition, the output charge QOSS has to be removed to enable blocking. This results in switching delays.
To achieve high breakdown voltages Ubd, an edge-termination structure may be used in a peripheral area surrounding the active area with active MOSFET-cells. However, the peripheral area requires chip area and thus increases costs. Further, the edge-termination structure and the peripheral area, respectively, may substantially contribute to the output charge QOSS and the output capacitance COSS, respectively, for example to more than 10% of the total output capacitance COSS. Furthermore, the alternating n- and p-doped pillar regions of the charge-compensation structure are typically formed as elongated strips when seen from above. Accordingly, the portions of the peripheral area which are arranged, in elongation direction of the alternating n- and p-doped pillar regions, between the active area and the lateral device edge may have a comparatively high share of the total output charge QOSS. Even further, charge imbalances introduced into the peripheral area during manufacturing may increase the output charge QOSS and the output capacitance COSS, respectively.
Accordingly, there is a need to improve semiconductor devices with charge compensation structures and manufacturing of those semiconductor devices.